1. Field of the Invention
The present invention relates to wet oxidation of solid hydrocarbon containing materials, such as shale, coal, tar sand, wood and waste particles, or catalyst particles, or both. More particularly, it relates to a method of controlling feed of any solid materials on a batch or periodic basis to a high pressure, high temperature reactor for such oxidation or other hydrocarbon reaction and removal of the unreacted solid material from the reactor so that additional hydrocarbon containing material may be added.
2. Description of the Prior Art
It has been the practice in extracting hydrocarbon fluids from hydrocarbon containing solids by a wet oxidation process to form the feed to the reactor as a substantially homogeneous slurry of the solid and water. Such a slurry may be more readily pumped than a heterogeneous mixture of such solids and water. The slurry is periodically charged to a reactor where hydrocarbon fluid is extracted at high temperatures and pressures by the water and oxygen, such as air, carbon monoxide or molecular oxygen. Efficient hydrocarbon fluid extraction in such a wet oxidation process requires pressures of from about 220 psi up to about 5200 psi and temperatures of from 350.degree. F. up to about 900.degree. F. or higher.
A slurry of solid hydrocarbon containing materials either homogeneous or heterogeneous, is formed by (1) comminuting or reducing the solids to relatively uniform particle sizes, and (2) mixing the reduced solids with enough liquid to form a pumpable viscous mixture, and generally, (3) adding a hydrocarbon fluid to assist formation and suspension of particles in such a slurry, and where required, to add necessary heat to carry out the reaction process.
A particular value of converting such solid carbonaceous materials to fluid hydrocarbons is that they are usable, directly as transportation liquids or for further hydrocarbon processing. It is known that both organic and non-organic compounds, such as those of sulfur, nitrogen, iron and other metals in such hydrocarbon-containing materials may be removed through solution in the water phase of the reacted mixture so that the hydrocarbon may be more easily converted, as by catalysis to more valuable products.
Slurries, formed as indicated, are particularly abrasive to pumps, conduits and valves that control admission of batch or discrete quantities of the mixture to a high pressure reaction chamber. These conduits and valves are essential to take the solid particles from atmospheric conditions to the reaction chamber pressures, and vice versa, to release and dispose of the hydrocarbon depleted residue, such as sand, shale or char. In particular, we have found that it is essential to maintain the slurry in a well mixed condition to control the amount and quality of particulate material charged to the reactor. For efficient operation the slurry desirably contains a high percentage of solids of from 5% to 90%, but preferably from 10% to 40%. However, such high concentrations of solids are difficult to hold in suspension and highly abrasive to the pumping system at such high pressures. Further, we have found that valves for such service which contain any obstructions to flow, such as valve seats, throats or stems, act as throttling elements and are easily destroyed by slight pressure differences across the valve while such a slurry is being transferred into or out of the pressure chamber. Similarly, check valves or gate valves forming flow restrictions relative to the flow conduits are subject to abnormal deterioration. Additionally variable volume chambers formed by flexible diaphragms or inflatable chambers, either external or internal to the slurry, present difficult maintenance and durability problems for long term operation of such a system.
Examples of such prior known systems for wet oxidation of hydrocarbon containing solids include: U.S. Pat. No. 4,211,174--Martin et al. This patent discloses a coal slurry system in which an aqueous slurry includes only 0.5 to 3 weight percent coal pulverized to a particle size not over about 0.02 inch. The slurry is then pumped by a high pressure pump into a reaction vessel through a plurality of check valves. U.S. Pat. No. 3,891,352--Tsukamoto, discloses a similar slurry pumping system employing check valves in two valve bodies to alternately pump the slurry in a pipe line.
U.S. Pat. Nos. 3,824,084--Dillon et al, and 4,174,953--Sun et al, disclose preparation of a coal slurry by pulverization and suspension in water to remove sulfur components by wet oxidation. U.S. Pat. No. 3,912,626--Ely et al is an example of wet oxidation of sewage sludge. U.S. Pat. No. 4,247,384-- Chen et al is directed to a method of liquefaction of wood or coal by wet oxidation. U.S. Pat. No. 4,013,560--Pradt discloses wet oxidation systems for incineration of combustible waste and power generation.
U.S. Pat. No. 4,174,280--Pradt et al, recognizes that certain organic containing solid materials are largely insoluble, immiscible and difficult to suspend or emulsify in water. The patentees propose to pump a very heavy slurry of liquid and solid with a cavity pump or a dry feeder into a high pressure reactor.
U.S. Pat. No. 4,100,730--Pradt also discloses energy recovery by wet oxidation of a combustible material, solid or liquid, from a water slurry. U.S. Pat. No. 4,197,090--Yoo et al discloses sulfur removal from a coal and water slurry by oxidation with heat and pressure. U.S. Pat. No. 3,876,497--Hoffman discloses a similar wet oxidation process to treat paper mill waste sludges. None of the foregoing patents recognize the problem of slurry feed and valve wear in batch or semi-continuous introduction of slurry into a high pressure and high temperature reactor, or removal of spent material from the reactor vessel.
Examples of systems disclosing use of diaphragm members for pumping solid material include: U.S. Pat. No. 4,106,533--Herzig. This patent discloses a high pressure (up to 365 psig) gasification system in which comminuted solid particles such as coal dust are fed through parallel tubes. Each tube includes an inflatable diaphragm actuated externally by hydraulic pressure means to supply particles to a screw conveyor feeding the gasification reactor. Rotatable gate valves open and close the ends of the parallel diaphragm tubes.
U.S. Pat. No. 3,393,944--Reintjes is directed to a plunger actuated feed chamber for a coal gasification system. The coal is in the form of pulverized dry solid particles. The plunger includes an elastomeric sleeve forming a diaphragm that may be expanded or contracted to pump the dry particles into a reaction chamber.
U.S. Pat. No. 4,159,150--Rachais discloses a lock hopper system for a subatmospheric pressure vessel such as a vacuum jet mill, used in grinding cement clinker to powder. The dry material flows by gravity and vacuum with the aid of vibrators.
Systems for hydraulically pumping abrasive slurries of solid particles using check valves include, U.S. Pat. No. 3,091,352--Tsukamoto and U.S. Pat. No. 4,304,527--Jewell et al.
U.S. Pat. No. 3,804,556--Katzer et al is directed to a mud pump using a floating piston hydraulic system in which a sliding valve is opened and closed in synchronism with the pump stroke for intake and discharge.